Comparative Analysis of Potassium Fractions in Surface Soils of National Open University of Nigeria (Noun) Research and Commercial Farms, Rigachikun, Kaduna State, Nigeria

A comparative study was conducted during the 2022 cropping season to evaluate the distribution of potassium (K) fractions in surface soils (0–20 cm) of the National Open University of Nigeria (NOUN) Research Farm and nearby commercial farms in Rigachikun, Kaduna State, Nigeria. A total of 24 composite samples (12 per farm) were collected using a randomized systematic design and analyzed for water-soluble, exchangeable, non-exchangeable, mineral, and total K, alongside selected physico-chemical properties. Baseline soil characterization showed that the soils were sandy loam (sand 64.2–67.1%, silt 20.4–22.3%, clay 12.5–13.5%), slightly acidic (pH 5.8–6.2), low in organic matter (1.45–1.82%), and had CEC values of 6.8–7.4 cmol/kg. Potassium saturation percentage (KSP) was 2.43% in the research farm (medium fertility) and 1.91% in the commercial farm (low–medium fertility). Potassium fractions were consistently higher in the research farm: water-soluble K (0.12 cmol/kg) exceeded the commercial farm (0.08 cmol/kg) by 50%; exchangeable K (0.18 vs. 0.13 cmol/kg) was 38.5% higher; non-exchangeable K (0.31 vs. 0.27 cmol/kg) was 14.8% higher; mineral K (1.21 vs. 1.08 cmol/kg) was 12% higher; and total K (3.74 vs. 3.45 cmol/kg) was 8.4% higher. Overall, the soils exhibited low potassium reserves, with the research farm maintaining relatively higher fertility than the commercial farm. The differences reflect variations in land use intensity and management practices. These results underscore the need for site-specific K fertilization, integrated nutrient management, and continuous monitoring to sustain productivity in Rigachikun.